Wireless communications is, in part, accomplished with the use of wireless base station transmit-receive systems. The purpose of a base station is to transmit and receive RF signals, such that they are properly routed to customers using, for example, a cellular telephone network. Base stations are coupled to antennas and amplifiers which are sometimes located more than 100 feet away from the base station itself. The antennas and amplifiers are coupled to base stations with coaxial cables.
In general, antennas are subject to lightning strikes. In the currently discussed setup, when an antenna or a nearby object is struck by lightning, a surge of electricity oftentimes travels through the coaxial cable to the base station. This surge of electricity can cause serious damage to the electronic components in the base station cabinet. Thus, the coaxial cable is typically first connected to a lightning protection device which is only then connected to the base station.
For the purposes of protecting a base station from damage caused by lightning, a protector, employing a quarter wave length bypass, referred to as a quarter wave length protector is employed. Another type of protector, known as a gas-discharge tube, is also utilized.
Typically, the protector is disposed between the coaxial cable line and the base station, which has components which can be damaged by a voltage surge.
A quarter wave length protector includes a portion of a transmission line having a length approximately equal to quarter wave length (.lambda./4) of the frequency of the desired signal traveling through the protector. The quarter wave length transmission line is connected between the signal conductor located within the coaxial cable and the external surface of the housing that contains the protector. The quarter wavelength protector acts like a parallel tuned resonance circuit, which exhibits a very high impedance in response to desired RF signals flowing through the signal conductor, and which exhibits a very low impedance in response to signals with low frequencies, such as those caused by lightening. Thus signals caused by lightening experience a short circuit path between the signal conductor inside the cable and the outer housing of the protector.
For gas-discharge type protectors, a gas-discharge tube is positioned between the signal conductor of the coaxial cable and outer housing of the protector. The gas inside the discharge tube is designed to be ionized by lightning surge voltage. The ionization creates a conductive path from the signal conductor inside the coaxial cable and the outer housing. In both cases, rather than the surge of electricity continuing to pass through the coaxial cable and into the base station, the short circuit allows the electricity to pass through the conductive housing of the protector. The housing of the protector is in electrical contact with the base station cabinet. Thus, the cabinet acts as a grounding surface, because as a relatively large metal plate, it is capable of dissipating the energy resulting from the lightning strike.
Coaxial cables are connected to other cables and components inside the base station cabinet, through the use of male and female connectors. In the art, female connectors are known as mating jacks and male connectors are known as plug connectors. Jacks have no moving parts. The outer conductor surface of a jack is fixed and threaded on its outer surface. Plugs, on the other hand, have a movable coupling nut, which is threaded on its inside surface.
Typically, the end of the lightning protector that couples to the base station, also referred as the equipment-side, terminates in a plug. This is due to the fact that a particular filter is often used in the base station which terminates in a jack. The other end of the lightning protector that couples to the coaxial cable terminates in a jack.
A protector having a plug on the equipment-side (i.e., the portion of the plug connected to electronics in the cabinet) can result in inefficient grounding. The noise current traveling on the outer shell of the plug to the cabinet surface will inductively couple back into the center conductor. Because the plug has a moving part, any discontinuity in the outer shell may establish a resistive path which may prevent current from being efficiently grounded. This discontinuity may cause electric arcs referred to as arc-over. Moreover, if the arc-over is severe, there is a fire hazard and the possibility of damage to the equipment. Ultimately the result is that the equipment is not properly protected. The moving part may also result in the varying electrical conductivity between the outer shell of the adapter and ground in different portions of the cabinet surface. In turn, proper quality assurance cannot be guaranteed. Finally, an additional problem is that noise and interference can also be caused by the discontinuity.
One way to overcome the aforesaid problems is to provide a protector that has mating jacks at both ends. In that event, one of the mating jacks is inserted inside the base cabinet through a hole and the other end engages with a coaxial cable that connects to the antenna. Since the jack of the protector does not have any moving parts, the housing of the protector and the cabinet surface from a good connection via the jack. A problem with this arrangement is that the filter used inside the base cabinet also terminates with a mating jack. Thus, in order to connect the filter's mating jack to protector's mating jack, there is a need for an adaptor cable that terminates with plugs at both ends. The adaptor cable can then be disposed between the two jacks.
In such a base station system, there is also a mechanical problem with the currently employed set-up. Due to the length of the coaxial cable, the cable is often twisted in such a way that a large torque is present where the cable must be connected to the base station. This interferes with the goal of obtaining a secure connection between the cable and the base station.
Thus, there is the need for an economical arrangement which prevents inefficient grounding of lightning voltage surges when utilizing lightning protectors with the plug-side of the adapter connected to the equipment.